This invention relates generally to a method for micro-texturing molds, and more particularly, to a method for micro-texturing steel molds used to form a variety of devices, in particular elastomeric devices, such as seals.
Seals are used in a variety of applications where the seal is subjected to a high level of friction. An example, of a seal being subjected to increased friction is a seal ring, which is used in applications, such as in a transmission, for preventing or substantially limiting the leakage of liquids and pressure loss from portions of the transmission. Generally, the known seal rings are for sealing transmission clutch packs and are xe2x80x9cwet sealsxe2x80x9d, that is, both the high pressure and low pressure faces or sides of the seal ring are exposed to or are in communication with a liquid, such as a transmission oil or similar lubricant. The rotating seal rings typically include at least one face or side that is positioned in an opposing, face to face relation with a non-rotating surface of the transmission case for forming a sealed or substantially sealed condition therewith. The known seal rings are generally made of a hard polymer.
When in use in an engine or transmission, for example, the seal ring will move or be contacted by a moving device so that the seal ring is subjected to either axial or circumferential or rotational friction resulting from the movement of the seal ring or a device in contact with the seal ring. Often the outer circumferential wall of the seal ring will be in contact with a non-rotating or stationary metal surface of the transmission case. As such, the seal ring will potentially be in frictional contact with the transmission case, with the friction potentially causing the seal ring to erode or breakdown. Also, the seal ring will often be placed around a moving member so that the inside circumferential wall of the seal ring is in contact with a moving member. This too will cause friction and potentially the eventual degradation of the seal ring. Because of the friction and stress that the seal ring is exposed to it is desired for the seal ring, as well as, other seals to be lubricated, specifically it is desired to increase the lubricity between a seal and the surfaces in contact with the seal so as to reduce friction.
While the seal ring is an example of a seal that can break-down because of friction, numerous other types of seals break-down as a result of friction. As such, it is desired to have a seal that can be lubricated. One way to increase the lubricity of a seal is to texturize the seal so that reservoirs or gaps are included in the seal construction, with the reservoirs holding an amount of oil. The oil will preferably leak away from the seal and lubricate the space between the seal and the surface contacted by the seal. It should be pointed out that the reservoir or texturing should not be too deep, otherwise the oil or other lubricant will not leak away from the seal. Instead the oil will be held in the reservoir or texturing of the seal, which will prevent the lubrication of the space between the seal and the surface contacted by the seal. Thus, it is desirable to have a method for forming a seal that is texturized or has small reservoirs or gaps included in its construction. It is further desired for the texturing of the seal to be of a sufficient size to cause lubrication between the seal and the surfaces contacted by the seal. More particularly, it is desired to have a method for micro-texturing a mold so that a seal having a micro-textured surface can be formed, with the micro-textured seal allowing for the lubrication of the space located between the seal and the surfaces contacted by the seal.
It should also be pointed out that until recently it was believed to be unknown to produce a texturized seal. Traditionally, it was believed that a seal should have a smooth surface. For this reason, methods for producing texturized seals have been unknown and, in particular, methods for producing a micro-textured seal have been unknown. Thus, it is desired to have methods for producing a micro-textured seal.
It has been known to acid etch steel molds so as to form a texture in a particular steel mold and form a textured finished product from the steel mold. To acid etch the steel mold, traditionally a photograph has been taken of the desired texture with a full-scale reproduction of the texture reproduced to form a mask used to etch the steel mold. The texture created by this method has typically been a macro-texture, in other words a texture designed for purposes other than holding a small amount of liquid. This method has not been intended to be used to micro-texture a steel mold to allow for production of a seal having a micro-texture surface. Thus, this method is generally not suitable for forming a mold that can produce a product having a micro-textured surface. Another problem is that full-scale reproductions are disadvantageous because the ability to etch certain patterns in steel molds has been limited. Thus, it is desired to have a method for acid etching a steel mold that does not involve a full-scale reproduction and that can etch a wider variety of patterns, in particular micro-textures.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention a method is practiced which allows for the production of a mold having a micro-textured surface. More particularly, the present invention relates to a method for producing a mold having a micro-textured surface whereby the mold can be used to form a seal having a micro-textured surface. It is especially preferred for the micro-textured surface to be located at a position on the seal whereby lubricant can be released so as to lubricate the space between the seal and a surface contacting the seal. As such, the resulting seal will advantageously hold a small amount of lubricant that can be slowly released when the seal is in use. The released oil will lubricate the interface between the seal and a surface or a movable part so that friction is reduced and hopefully the life of the seal is increased.
It is believed that it has not been known in the past to micro-texture a seal, as such methods for producing a micro-textured seal are believed to be unknown. To produce a seal having a micro-textured surface a mold must be produced which can be used to form the micro-textured seal. However, methods for imparting a micro-texture construction to a mold used to form a seal have been unknown. Thus, the present invention relates to a method for producing a mold having a micro-textured surface.
The method is initiated by developing an image of a desired micro-texture surface. Any image can be developed so long as the resulting micro-texture surface in the mold will allow for production of a seal that holds an amount of oil that will lubricate the interface between the seal and the wall or any other structure contacted by the seal, while still allowing the seal to prevent leakage of liquids. It is important that the image allow for production of a micro-textured seal that reduces the friction between the seal and either a wall or moving part by releasing an amount of lubricant. Preferably, the image when transferred to a mold will result in a rough or textured surface on a seal, with the surface having a plurality of peaks and valleys, so that the depth of the texturing will range between about 0 microns and about 500 microns. The image can be computer generated or can be taken from an actual surface.
After the image is developed it is necessary to transfer the image to a mold, so that the image results in the mold having a micro-texture surface. A variety of means can be used to transfer the image, including a variety of photoresist techniques. Generally, the image can be used to form a mask, with the mask then used to etch the surface of the mold and thereby micro-texture such surface. More preferably, the image is used to create a photograph negative, with the negative placed on a photosensitive plate. The negative will then be developed on the photosensitive plate. Wax will next preferably be applied to the photosensitive plate, with the wax only adhering to the exposed areas of the plate. The exposed areas are those areas which are not to be etched, meaning that the exposed areas are those areas where a valley on the surface will not be formed. The wax is preferably transferred by contact paper to a mold. Next the mold will be submerged in an acid bath so that the acid will etch the mold and form the micro-texturing on the mold surface. Preferably, the mold is made of steel. After a sufficient time in the acid bath, the mold will have a micro-texture surface and will be suitable for use in forming a seal.
The present invention is advantageous for a number of reasons. First, it allows for a method for micro-texturing a mold used to form a seal. It has previously been difficult to micro-texture molds used to form a seal, and in fact it has been previously unknown to produce seals having a micro-texture surface. The present method is also easily and relatively inexpensively performed. Advantageously, the present method results in a mold that can form a seal that lubricates the interface between the seal and a surface contacted by the seal and that does not allow for liquids to leak.